In the lithography art, a highlight is recently put on the organic solvent development again. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkaline development and organic solvent development is under study.
As the resist composition for negative tone development with organic solvent, positive resist compositions of the prior art design may be used. Such pattern forming processes are described in Patent Documents 1 to 3. These patent documents disclose resist compositions for organic solvent development comprising a copolymer of hydroxyadamantane methacrylate, a copolymer of norbornane lactone methacrylate, and a copolymer of methacrylate having acidic groups including carboxyl, sulfo, phenol and thiol groups substituted with two or more acid labile groups, and pattern forming processes using the same.
Further, Patent Document 4 discloses a process for forming a pattern through organic solvent development in which a protective film is applied onto a resist film. Patent Document 5 discloses a topcoat less process for forming a pattern through organic solvent development in which an additive is added to a resist composition so that the additive may segregate at the resist film surface after spin coating to provide the surface with improved water repellency.
The negative tone pattern forming process is also useful in enhancing the resolution of trench patterns. Since a high optical contrast is available where the pattern design on the mask is isolated lines (i.e., bright-field mask), as compared with where the pattern design on the mask is isolated trenches (i.e., dark-field mask), the negative tone patterning process involving reversal of line image is more advantageous in forming trench patterns. See Non-Patent Document 1.
However, since the organic solvent development is unlike the conventional positive tone development, at a device supplier's manufacturing site or the like, the negative tone pattern forming process has not completed transition to the in-line development system wherein the exposure tool is directly connected to the organic solvent developing unit. In such cases, the negative tone development is performed by an off-line development system. Namely, after PEB, the wafer is transferred to a separate development unit where development is carried out.
In the off-line development system, there is a lapse of time, known as post exposure bake to development delay (PEBDD) or post PEB delay (PPD), until the wafer is transferred to the separate development unit. Since the acid generated in the exposed region of resist film is kept in the state that it has been diffused by PEB, the acid will diffuse into the unexposed region during the delay, until the start of development.
It is pointed out in Non-Patent Document 2 that the diffusion of acid into the unexposed region during PPD causes shrinkage of the critical dimension (CD) of a pattern. It is also empirically known that a change of pattern profile concomitant with the shrinkage of CD leads to the degradation of lithography performance as evidenced by an edge roughness increase.
The amount of CD shrinkage due to PPD varies with a lapse of time. The PPD is not consistent depending on a particular progress of operation at a manufacturing site. It is important how to reduce a change with the lapse of time. There is a strong demand for a resist composition which is satisfactory in lithography performance and experiences a minimal CD shrinkage and a minimal change of pattern profile during PPD.
Citation ListPatent Document 1:JP-A 2008-281974Patent Document 2:JP-A 2008-281975Patent Document 3:JP 4554665Patent Document 4:JP 4590431Patent Document 5:JP-A 2008-309879Patent Document 6:JP-A 2010-215608(US 20100209827)Non-Patent Document 1:Proc. SPIE Vol. 7639, 76391Q(2010)Non-Patent Document 2:Proc. SPIE Vol. 8682, 86821P(2013)